1. Field of the Invention
The present invention pertains to an apparatus including a high frequency, unbuffered, voltage controlled oscillator for transmitting radio frequency or so called microwave signals through a coaxial conductor or waveguide structure, which may comprise a portion of a fluid pipeline or the like, for sampling the composition of mixtures of substances as a function of the dielectric properties thereof. In particular, the concentration of small quantities of liquids such as water in liquids such as oil are measured by comparing the change in the output signal of the oscillator with signals corresponding to known concentrations or compositions of mixtures.
2. Background
Various types of apparatus have been proposed for measuring the concentration of one substance in another, particularly the concentration of a liquid or flowable substance in another liquid or flowable substance. One technique which is useful utilizes radio frequency or microwave energy measurement. Various devices which utilize the broad concept of determining composition of matter by measuring changes in a microwave signal are disclosed in U.S. Pat. Nos. 3,498,112 to D. D. Howard; 3,693,079 to C. W. E. Walker; 4,206,399 to H. G. Fitzky, et al; 4,311,957 to S. J. Hewitt et al; 4,361,801 to W. Meyer et al; 4,240,028 to L. A. Davis, Jr.; 4,352,288 to H. J. Paap et al; 4,499,418 to D. A. Helms et al; 4,367,440 and 4,429,273, both to R. P. Mazzagatti.
Although various systems utilizing microwave transmissivity or signal alteration characteristics have been proposed in the prior art, certain considerations in utilizing microwave energy to detect the presence of the concentration of one medium in another have not been met by prior art apparatus. In particular, it is desirable in certain instances to be able to accurately measure, on a continuous basis, the concentration or change in concentration of one fluid in another and particularly where the concentration of one fluid is a very low percentage of the total fluid flow rate or fluid mixture quantity. It is also desirable that the signal change caused by the presence of one substance or medium in another be easily measured and be relatively error free, again, particularly in instances where measurements of low concentrations of one substance such as a fluid in another substance such as another fluid are being taken. Moreover, it is important to be able to transmit the microwave signal through a true cross section of the composition being sampled or measured to enhance the accuracy of the measurement.
One relatively important application of microwave energy for measuring the properties of a fluid mixture is in the transportation and handling of crude or refined oils wherein it is desirable to measure the concentration of water or some other fluid in the oil. In this instance, relatively small concentrations of water or other fluids are usually found in the oil being transported after preliminary processing or separation procedures are carried out. However, in some transport systems such as in the Trans-Alaska Pipeline System, the very large quantities of oil being transported make it highly desirable to be able to make accurate measurements of the percentages of other fluids present in the oil, such as water, so that separation and treatment facilities can be adjusted to accomodate the presence of the water and tariffs for transporting the oil can be adjusted accordingly.
Therefore, it has been considered desirable to develop a microwave based system for determining the concentration of water in oil, for example, in various quantities as a percent of the total flow. It is to this end that the present invention has been developed with a view to providing an improved apparatus for determining the concentration of one medium in another, such as water or other liquids in crude or refined mineral oils.